Let's see, the worst maps for me would have to be, in no particular order: Bunker (TS: FP), Robot Factory (TS2 Arcade Version), and Tomb (TS1 Arcade Version).
The thing about Tomb, though, is that I do not actually dislike the map, and have had a lot of fun playing frantic matches over the years. It's just that so much of the map was blocked off in Arcade, and it really could have benefited from having more Story areas accessible. It's the cramped nature of the Arcade version that makes it not as good as the other Story maps in TS1 that were fully brought over into Arcade Mode.